3605 Estimating human error probabilities in quantitative risk assessment

Overview:

Human error plays a role in over half of major incidents, occurring across all stages of a system’s life cycle—from design and manufacturing to operation and decommissioning. As such, assessing the human contribution to risk is essential.

For over 40 years, safety professionals and regulators have worked to estimate and reduce both technical and human failure probabilities. Whilst human error assessment methods may seem straightforward, applying them credibly requires significant expertise.

This guide supports the generation of credible human error probability (HEP) estimates, drawing on four decades of practical experience with established methods. It addresses common challenges encountered during project execution, peer review, and regulatory scrutiny, offering guidance on method selection, application, and supporting evidence for independent assessment.

It covers the following topics:

• A description of the stages of quantified human reliability assessment.
• Introduction to HEPs and other key terminology.
• How the quantitative analysis should interface with qualitative analysis and technical analysis.
• Selecting appropriate HEP methods.
• General guidance on estimating HEPs
• Qualifications needed for HEP estimation.
• Human dependence and how it affects HEP estimates.
• Ensuring adequate substantiation.
• Meeting regulator expectations.